A flow cytometer used in medical and biological fields includes a fluorescence detection device that receives fluorescence emitted from a fluorochrome attached to a measurement object by irradiation with a laser beam to identify the type of the measurement object. Particularly, in recent years, attempts have been made to perform fluorescence measurement using fluorochromes to examine intracellular local information such as proteins.
In order to examine intracellular local information, it is necessary to achieve higher measurement resolution than ever before.
As described in the online article “Introduction to Principles of FCM-V,” which could be found at http://www.bc-cytometry.com/FCM/fcmprinciple—5.html#5-1 and http://www.bc-cytometry.com/FCM/fcmprinciple—6-1.html on Nov. 28, 2007, a currently-used flow cytometer includes a flow cell (flow cell body). The flow cell is a hollow chamber made of quartz and elongated and having a rectangular cross-section. The flow cell transmits a laser beam and is used to irradiate cells contained in a sample with a laser beam. When passing through a measurement point in the flow cell, a measurement object is irradiated with a laser beam passing through the flow cell, and fluorescence is detected by a detection system provided separately from the flow cell.
The aforementioned online article “Introduction to Principles of FCM-V” describes the following. The light intensity of a laser beam has a Gaussian distribution. The laser beam is focused to an elliptical cross-section to increase its light intensity and to achieve an optical system capable of preventing two or more cells from being coincidentally irradiated with a laser beam. Before reaching a sample stream containing cells, the laser beam passes through two first and second cylindrical collecting lenses to be focused to an elliptical cross-section. The first cylindrical collecting lens is provided to adjust the width of a laser beam, and the second cylindrical collecting lens is provided to adjust the height of a laser beam. The laser beam focused to an elliptical cross-section by passage through the two lenses irradiates a cell flowing through a slim flow cell having a rectangular cross-section. The sample stream becomes narrower by reducing the sample pressure, which makes it possible to allow a cell to pass through the center of a laser beam where fluctuations in light intensity are smaller, thereby improving measurement resolution.
However, the flow cytometer described in the aforementioned online article “Introduction to Principles of FCM-V” has a problem in that its measurement resolution cannot be improved to such an extent that intracellular local information such as proteins can be examined.